My 97 STS HVAC system decided to act up and now blows cold out of the right dash vents, hot out of the left dash vents and the back seat vents. I have run the temp control to max hot and cold several times, hoping to shake loose a stuck door. I have turned the passenger temp control off and on and run that from hot to cold also. Turning the AC on and off also makes no difference. What is the root cause of this problem?

 

Check the freon level first.
Believe it or not that is the most common cause of the cold side hot side condition.

 

Thanks for the tip! I expected a stuck heater door actuator or some silly control module that will require disassembly of the entire vehicle to get to it. I recently installed a new compressor and was a little light on the 134 fill.

 

Does the hot cold have same symptoms when you want heat not AC, I have just bought 97 sts, I wanted heat on driver side, got cold driver and hot passenger, just wondering if makes differince when calling for heat and not AC
Getting cold here in Iowa want heat not ac
thanks

 

No, a low freon charge will not effect the heater.
Sounds like a mix door problem.

 

This is a heater core air lock or heater core seal tab blockage, heater core is hot on the top but cold on the bottom, it needs flushing or filling manually when cool, elevate front of car before doing this.